I didn't know putting parenthesis around a statement, excluding the order
by, could make any difference. There have been times when I get a few
results against a larger table, then I remember that I forgot the "order
by", so I add it and I watch it take much longer to produce the results.
In my mind, I say, why doesn't it just generate the results it did last
time, and then order those results, rather than sorting the whole table to
give me a sorted short list. Is this a trick I could use to improve query
performance when needing an unindexed sort order with a small result list?
From: Gerald Magnuson <gmagqcy.midrange@xxxxxxxxx>
To: midrange-l@xxxxxxxxxxxx
Date: 06/18/2015 02:08 PM
Subject: sql - why doesn't the query engine know this???
Sent by: "MIDRANGE-L" <midrange-l-bounces@xxxxxxxxxxxx>
so I have a bill of material query (parent, child) joining to a item
master file (twice, once on parent, once on child) and a status file(
joined on parent)... I want the list ordered by parent...
select parent,child,t02.desc,t03.desc,osipo# from
plan_bill t01
join items t02 on t02.item = t01.parent
join items t03 on t03.item = chlid
join ordstatus t04 on ositm# = t01.parent
where
parent like '%MTG%' and
child like 'S%' and
osid = 'OS'
order by bprod ;
I have built all advised indexes, and when I run it takes 30 minutes to
return 800 records.
however, when I take off the order by, it runs in 2 seconds.
then, I tried: (parens around select statement)
(select parent,child,t02.desc,t03.desc,osipo# from
plan_bill t01
join items t02 on t02.item = t01.parent
join items t03 on t03.item = chlid
join ordstatus t04 on ositm# = t01.parent
where
parent like '%MTG%' and
child like 'S%' and
osid = 'OS' )
order by bprod ;
and that ran in 2 seconds...
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